1. Field of the Invention
The present disclosure relates to a light beam emission apparatus, an optical scanning apparatus equipped with the light beam emission apparatus, and an image forming apparatus.
2. Description of the Related Art
In an electrophotographic image forming apparatus, such as a copying machine or a laser beam printer, an electrostatic latent image is formed on a photosensitive member by projecting a light beam from a light source to the photosensitive member, the latent image is developed by toner, a visible toner image is transferred to a recording material, and the transferred image is fixed to the recording material.
In such recent image forming apparatuses, a problem has arisen that dust particles invade the optical scanning apparatus, which includes the light beam emission apparatus, and the dust particles adhere to the optical components, such as a rotary polygonal mirror, lenses, or mirrors, thus obstructing reflection and transmission of the light beam, and reducing the image quality. With regard to this problem, Japanese Patent No. 4139030 discusses a configuration designed to improve the dust-proof performance of the optical scanning apparatus.
The optical scanning apparatus discussed in Japanese Patent No. 4139030 will be described in detail with reference to FIG. 11. A laser beam emission apparatus 900, which is mounted in the optical scanning apparatus, includes a laser element 901 (light source), a laser holder 902 configured to hold the laser element 901, a control drive circuit 903, a collimator lens 904, and an aperture 905. The laser element 901 is held by being fitted into a hole in the laser holder 902. The collimator lens 904 is fixed to a support member extending from the laser holder 902.
An elastic member 906 is arranged between the laser holder 902 and the aperture 905, and an elastic member 907 is arranged between the laser element 901 and the laser holder 902. With this configuration, dust particles are prevented from invading the laser beam emission apparatus 900.
However, the problem with the optical scanning apparatus discussed in Japanese Patent No. 4139030 is that when the laser element 901 is press-fitted into the laser holder 902, scraped chips of the laser holder 902, produced by abrasion with the laser element 901, adhere to the collimator lens 904. This problem will be described in detail with reference to FIGS. 12A, 12B, 12C, and 12D.
A case where the elastic member 907 is provided on the laser element side will be described. FIGS. 12A and 12B are sectional views of the laser beam emission apparatus 901, in which the elastic member 907 is provided or mounted on the side of the laser element 901. FIG. 12A illustrates a state before the start of press fitting of the laser element 901. FIG. 12B illustrates a state immediately after the start of press fitting of the laser element 901.
During assembling of a laser beam emission apparatus 900, conventionally, the laser holder 902 is fixed vertically, and then the laser element 901 is press-fitted into the laser holder 902 in the direction of gravitational force. The elastic member 907 is an annular-shaped member formed with such an external diameter slightly smaller than that of the laser element 901 as to prevent a foreign substance from being trapped inside when the laser element 901 is press-fitted into the laser holder 902. When the laser element 901 begins to be press-fitted into the laser holder 902, the inside wall of the laser holder 902 is scraped by the peripheral edge of the laser element 901, thus producing scraped chips. Just after the start of press-fitting of the laser element 901, because the elastic member 907 is not yet in contact with the laser holder 902, the scraped chips pass below the elastic member 907 and then adhere to a lens body tube 902a of the laser holder 902. When the collimator lens 904 is mounted to the laser beam emission apparatus 900 with the scraped chips adhering to the lens body tube 902a, during the assembling process or during a subsequent transport of the laser beam emission apparatus 900, the scraped chips adhering to the lens body tube 902a will come off and adhere to the collimator lens 904.
Another case where the elastic member 907 is provided on the laser holder side will now be described. FIGS. 12C and 12D are sectional views of the laser beam emission apparatus 900 when the elastic member 907 is provided or mounted on the side of the laser holder 902. FIG. 12C illustrates a state before the start of press-fitting of the laser element 901, and FIG. 12D illustrates a state just after the start of press-fitting of the laser element 901.
The elastic member 907 is an annular-shaped member formed to have such a height lower than the start position of press-fitting of the laser element 901 as to prevent a foreign substance from being trapped inside when the laser element is press-fitted into the laser holder 902. When the laser element 901 begins to be press-fitted into the laser holder 902, the inside wall of the laser holder 902 is scraped by the peripheral edge of the laser element 901, thus producing scraped chips. Just after the start of press-fitting of the laser element 901, because the elastic member 907 is not yet in contact with the laser holder 902, the scraped chips pass above the elastic member 907 and then adhere to a lens body tube 902a of the laser holder 902. When the collimator lens 904 is mounted to the laser beam emission apparatus 900 with the scraped chips adhering to the lens body tube 902a, during the assembling process or during a subsequent transport of the laser beam emission apparatus 900, the scraped chips adhering to the lens body tube 902a will come off and adhere to the collimator lens 904.
As described above, if the laser element, including the collimator lens with scraped chips adhering to it, is press-fitted into the laser holder, the light beam about to pass through the collimator lens 904 is obstructed, degrading the image quality.
When the laser beam emission apparatus having scraped chips adhering to it is mounted to the optical scanning apparatus, it is likely that the scraped chips are dispersed inside the optical apparatus by a flow of air caused by the rotation of a rotary polygonal mirror in the optical scanning apparatus, and the scraped chips adhere to the lenses and mirrors, reducing the image quality.